I22.9 ICD-10-CM Code: Subsequent ST elevation (STEMI) myocardial infarction of unspecified site
I22.9 maps to CMS-HCC V28 228 (RAF 0.252). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC Buddy coding tools
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FY 2026 Apr update / Diseases of the circulatory system (I00-I99) / Ischemic heart diseases (I20-I25)
I22.9
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceSubsequent ST elevation (STEMI) myocardial infarction of unspecified site
A second heart attack within 4 weeks of the first one where the specific location cannot be determined, with ST segment elevation.
Buddy Insight
Subsequent STEMI of unspecified site represents a documentation gap where a recurrent myocardial infarction within 4 weeks is documented but the wall location is not specified.
CMS-HCC V28
MappedHCC 228
RAF 0.252
CMS-HCC V24
MappedHCC 86
RAF 0.195
ACA/HHS
MappedHCC 131
Varies by metal level
ESRD/PACE
MappedHCC 86
RAF 0.151
RXHCC
MappedHCC 188
RAF 0.052
Code Book Path
Inclusion Terms
Official- Subsequent acute myocardial infarction of unspecified site
- Subsequent myocardial infarction (acute) NOS
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for I22.9 in this effective period.
Related Child Codes
Includes
Official- acute myocardial infarction occurring within four weeks (28 days) of a previous acute myocardial infarction, regardless of site
- cardiac infarction
- coronary (artery) embolism
- coronary (artery) occlusion
- coronary (artery) rupture
Excludes 1
Official- subsequent myocardial infarction, type 2 (I21.A1)
- subsequent myocardial infarction of other type (type 3) (type 4) (type 5) (I21.A9)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for I22.9 in this effective period.
Use Additional
Official- code, if applicable, to identify:
- exposure to environmental tobacco smoke (Z77.22)
- history of tobacco dependence (Z87.891)
- occupational exposure to environmental tobacco smoke (Z57.31)
- status post administration of tPA (rtPA) in a different facility within the last 24 hours prior to admission to current facility (Z92.82)
Code Also
OfficialICD-10-CM does not list Code Also instructions for I22.9 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is I22.9 an HCC code?
Yes. I22.9 (Subsequent ST elevation (STEMI) myocardial infarction of unspecified site) maps to Acute Myocardial Infarction under the CMS-HCC V28 risk adjustment model (and Acute Myocardial Infarction under V24), with a community non-dual aged RAF of 0.252. It is billable for payment year 2026.
Coder answer: I22.9 is billable and maps to V28 HCC 228, Acute Myocardial Infarction. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- I22.9
- Description
- Subsequent ST elevation (STEMI) myocardial infarction of unspecified site
- HCC (V28)
- HCC 228 — Acute Myocardial Infarction
- RAF
- 0.252
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
Work I22.9 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for I22.9
For I22.9 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed I22.9 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
I22.9 is the ICD-10-CM diagnosis code for subsequent st elevation (stemi) myocardial infarction of unspecified site. A second heart attack within 4 weeks of the first one where the specific location cannot be determined, with ST segment elevation. I22.9 sits in the ICD-10-CM chapter for diseases of the circulatory system (i00-i99), within the section covering ischemic heart diseases (i20-i25).
Under the CMS-HCC V28 risk adjustment model, I22.9 maps to Acute Myocardial Infarction (HCC 228) with a community, non-dual, aged base RAF weight of 0.252. Under the older V24 model, I22.9 mapped to the same category but with a base RAF weight of 0.195, V28 recalibrated weights across the entire model. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
Query the provider for the specific wall location of the subsequent MI before using this unspecified code. Because I22.9 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for I22.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Query the provider for the specific wall location of the subsequent MI before using this unspecified code
- •This code should be used only when the location truly cannot be determined from available documentation
Clinical Significance
Subsequent STEMI of unspecified site represents a documentation gap where a recurrent myocardial infarction within 4 weeks is documented but the wall location is not specified. While it still captures the HCC value, this code should prompt the coder to query the provider for site specificity, as electrocardiogram findings typically reveal the involved territory.
Documentation Requirements
- ✓Documentation of a recurrent acute myocardial infarction within 4 weeks
- ✓STEMI pattern confirmed on electrocardiogram
- ✓Re-elevation of cardiac biomarkers
- ✓Evidence that the specific wall location cannot be determined from available records
- ✓Both initial and subsequent myocardial infarction codes must be assigned
Commonly Confused Codes
- •I22.0: Subsequent STEMI of anterior wall: preferred when anterior wall is documented
- •I22.1: Subsequent STEMI of inferior wall: preferred when inferior wall is documented
- •I22.8: Subsequent STEMI of other sites: preferred when other specific sites are documented
- •I21.3: Initial STEMI of unspecified site: for the first event, not recurrence